The present invention relates to a gravure printing method using aquatic gravure ink and a printing drum, print material, and equipment such as an ink pan, a furnisher roll, and a doctor knife used for carrying out the method.
Conventionally an organic solvent type of (oil) ink has been used in the gravure printing, and for color matching, printing is performed once or repeatedly in the overlaid state using process color ink in which coloring materials for indigo blue, red, yellow, black and white colors are included. When a specific color is required by a customer, toning is performed to satisfy the customer""s request. If a large quantity of ink with any specific color is required, a printing firm purchases the ink already toned, by an ink manufacturer, from the supplier. Because of the characteristics of the organic solvent type of ink, to satisfy a customer""s requests for coloring performance and gradation, generally a low-mesh (with about 175 lines) and deep (with the depth of 18 to 30xcexc) printing plate is used.
For the reasons described above, the problems as described below occur in the gravure printing method using the organic solvent type of gravure ink.
1) As the ink is of an organic solvent type, problems occur concerning the working environment in the printing firms, accident prevention, contamination of the environment due to the emission of the gasified solvent to atmosphere. Further, there is the problem of residual solvents, when the material printed with the ink is used as a film for food packaging.
2) When the organic solvent type of ink is used, as the ink dries fast and the gradation in printing is narrow, a deep and low-mesh printing plate is used as described above. In this case a large quantity of ink is consumed. This is a main cause for cost increase in printing.
3) In the conventional gravure printing, printing with the process color ink as described above is performed once or repeatedly, and further as ink with a specific color (required by a customer) is used in many cases, a number of colors and the number of printing plates increase. This results in a time loss due to preparatory steps before the start of printing and a toning loss. Further in a case of ink with a specific color, as the ink can not be used for other purposes, the quantity of left over remaining ink increases. This negatively effects printing cost. Sometimes the remaining ink is discarded, so that improvements are required also from the view point of resource saving.
4) Recently customers in the market require various types of print materials with a small lot to be produced and in addition within a short period of time. With this, the needs for cost management are becoming more and more stringent. Further social attention is more and more concentrated on the problems concerning environmental pollution and sanitary management in food industries. When organic solvent types of ink are used, the social needs cannot be satisfied.
For the reasons described above, a printing method using aquatic gravure ink in place of the organic solvent type of ink is being considered with keen interest. Further, different from the oil gravure ink conventionally used in the art, the aquatic gravure ink insures substantial improvement in the working environment in the printing firms. Because of this feature, it can be expected that the aquatic gravure ink will be used more and more in gravure printing.
When the aquatic gravure ink is used, the problems caused in association with use of organic solvents do not occur. However, aquatic ink has by its nature such deficiencies including the hardness in drying, hardness in resolving in the water solvent, and hardness in wetting a printing plate surface due to the surface tension. When the type board is set by the same technique as that with the organic solvent type of ink currently available in the market, the printing speed becomes lower. In addition such problems as fogging or gradation fault occur on the printing plate, which makes it impossible to obtain high quantity print materials.
2. In the conventional type of gravure printing machine, the size of the ink pan 1 is very large as shown in FIG. 5, a large quantity of remaining ink is left in the ink pan 1 (about 20 kg per printing plate). When the ink is the standard color, the ink can be used the next time. However, if the ink is a specific color based on the customer""s request, it is necessary to stock the ink until the ink is used the next time. This results in substantial a cost increase.
Especially, when structure of a printing machine using aquatic gravure ink is as described above, due to fogging on the type board caused by hardness of the ink in resolving in a water solvent as an intrinsic defect of aquatic gravure ink, the remaining ink can not be used again, which causes a grave problem in cost management.
In FIG. 5, designated at the reference numeral 2 is a furnisher roll, at 3 is a printing drum, at 3a is a printing plate surface, at 5 is a doctor blade, at 6 is a pressure drum, and at 7 is a film.
In the conventional type of gravure printing machine, the furnisher roll 2 is provided in the side opposite to the doctor as shown in FIG. 6. Because of this configuration, when gravure printing is carried out with aquatic gravure ink, wetting failure as an intrinsic defect of the aquatic gravure ink occurs due to the surface tension on a surface of the printing plate, so that, as the printing speed becomes faster, ink on the printing plate drops into the ink pan 1, which causes blurring on print materials or fogging on the printing plate surface and disadvantageously makes it difficult to perform printing under good conditions.
Further in the conventional doctor knife of gravure printing machine, the length L of a back plate 5b projecting from a bracket 5a of the doctor blade 5 is set to 30 m/m as shown in FIG. 7 and FIG. 8, and the length L1 of a blade tip of a doctor knife 5c is set to 4 m/m, so that, because of the dimensions, the excellent coloring performance to and gradation on a base film are insured when the printing ink is oil ink.
However, when printing is performed with aquatic gravure ink under the same conditions as those employed when printing is performed with oil gravure ink, fogging occurs on a surface of the printing plate due to the doctor cutting fault caused in association with the hardness of the ink in resolving in a water solvent as an intrinsic defect of the aquatic gravure ink, and there occurs the problem that printing cannot be carried out without changing structure of the doctor.
3. In the gravure printing machine using oil ink, as shown in FIG. 11, the furnisher roll 2 is provided against the printing drum 3 in the side opposite to the doctor knife 5, and ink 4 in the ink pan 1 is pumped up by the single furnisher roll 2 and supplied onto the printing plate surface 3a. In FIG. 11, designated at the reference numeral 6 is a pressure drum, and at 7 is a printed film.
When gravure printing is performed using the aquatic gravure ink, if the conventional structure is unchanged, wetting failure of ink 4 occurs on the printing plate surface 3a due to the surface tension as an intrinsic defect of the aquatic ink, and as the printing speed becomes faster, the ink 4 supplied onto the printing plate surface 3a drops into the ink pan 1, and as the result, blurring on print materials and fogging on the printing plate occur, which disadvantageously makes it impossible to perform printing under good conditions.
When gravure printing is performed using the oil gravure ink, the problem described above does not occur, but such problems as blocking occur when the printing plate surface 3a is dried after the ink is transferred onto the film 7, and to prevent this phenomenon, it is necessary to pump up the ink 4 from the ink pan 1 as fast as possible, and to satisfy this necessity, the furnisher roll 2 is provided in the opposite side from the knife edge 5. When the printing drum 3 is rotated at a faster speed, the ink 4 drops or scatters from the surface 3a of the printing drum 3 due to the centrifugal force and weight of the ink 4, so that there is a limit to increasing the rotating speed of the printing drum 3 even when the oil gravure ink is used.
4. In the gravure printing machine using oil ink, ink 4 in the ink pan 1 is pumped up by the furnisher roll 2, and surplus ink transferred onto the printing drum 3 is scraped off by the single doctor knife 5 to form the excellent printing plate surface 3a as shown in FIG. 14. With this, good prints are obtained on the base film 7 via the pressure drum 6.
The blade tip 5c of the doctor knife 5 is generally supported by the back plate 5b and clamped or fixed with the bracket 5a as shown in FIG. 15.
When gravure printing is carried out using aquatic gravure ink and with the conventional type of doctor knife 5 having the structure as described above, the wetting failure of the printing plate surface 3a occurs, caused by large surface tension and the doctor cutting fault due to precipitation of not-resolved materials onto the printing plate surface 3a because of the hardness of the aquatic ink in resolving in a water solvent. Blurring on print materials or xe2x80x9cfogging on the printing platexe2x80x9d is generated, which disadvantageously makes it difficult to carry out printing under good conditions.
Especially when black ink (with carbon contained therein) or white ink (containing titanium white) is used in printing, the remarkable defect of precipitation of not-resolved materials as described above is generated.
When a doctor pressure to the printing drum 3 is made larger to solve the problems described above, the effect is maintained within a short period of time, but as the doctor knife wears out quickly, so that sharpness in cutting with the doctor knife deteriorates, xe2x80x9cprinting plate foggingxe2x80x9d occurs. This makes it impossible to continue the printing job for a long period of time, and in addition, the type set on the printing plate surface 3a becomes worn out. Disadvantageously, a new gravure cylinder is required.
Therefore, and as the final means for solving the problems as described above, when printing is performed with aquatic gravure ink and with the conventional type of doctor knife, the way to continue the printing job is by lowering the printing speed.
It is a first object of the present invention to provide an aquatic gravure printing method capable of providing high quality aquatic gravure prints by solving the problems of printing plate fogging or gradation faults generated when printing is performed with aquatic gravure ink, and to provide a printing drum used for carrying out the method, and to provide prints printed by the method.
It is a second object of the present invention to enable reduction of ink cost by reducing a quantity of remaining ink as much as possible in an ink pan of a gravure printing machine using aquatic or oil gravure ink.
It is a third object of the present invention to provide a furnisher roll not causing wetting failure even when rotated at a high speed in a gravure printing machine using aquatic ink.
It is a fourth object of the present invention to provide a doctor blade or doctor knife which does not cause fogging on a printing plate in a gravure printing machine using aquatic gravure ink.
It is a fifth object of the present invention to provide a furnisher roller to solve the problems of xe2x80x9cblurringxe2x80x9d or xe2x80x9cfogging on a printing platexe2x80x9d due to wetting failure in gravure printing carried out by using aquatic gravure ink.
It is a sixth object of the present invention to provide a furnisher roll to enable running of an oil gravure printing machine at a higher speed as compared to that based on the conventional technology.
It is a seventh object of the present invention to provide a doctor knife unit which will neither cause xe2x80x9cblurringxe2x80x9d on print material nor xe2x80x9cfogging on a printing platexe2x80x9d due to a doctor knife cutting fault due to wetting failure or hardness in resolving.
According to the invention, a gravure printing method is provided for printing characters or patterns with desired colors and tones on a base material with a printing drum set with 200 to 400 mesh lines and the depth in the range from 10 to 17xcexc and by using process color of aquatic gravure ink in which coloring materials for indigo blue, red, yellow, black, and white colors are printed once or repeatedly in the overlaid state.
According to another aspect of the invention, an ink pan structure and arrangement for a gravure printing machines using aquatic or oil gravure ink is provided. The ink pan structure has an ink pool sized for only a furnisher roll to be dipped therein and a cooperating printing drum is always maintained outside the ink pool.
According to another aspect of the invention, a furnisher roller unit and arrangement for a gravure printing machine is provided. The unit includes a plurality of furnisher rollers.
According to another aspect of the invention, a doctor knife unit and arrangement for a gravure printing machine is provided. The unit includes a plurality of doctor knives.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.